sr-iov: virttest.test_setup: Try to get more pxception when VF/Pf clean up command fail.

Also delete self.dev_unbind_drivers.

Signed-off-by: Feng Yang <fyang@redhat.com>
virttest.test_setup: Add devices parameter for get_pf_devs() and get_vf_devs()

Signed-off-by: Feng Yang <fyang@redhat.com>